Phytoestrogens, widespread plant compounds, have been proposed as protective agents against hormone dependent cancers in humans, but results from human studies are inconclusive. Their main two subclasses are isoflavones (soy and soy products) and lignans (whole grains, fruit and vegetables). Because of their possible preventive potential, large-scale prospective studies are needed to clarify the issue of phytoestrogens and cancer. The European Prospective Investigation into Cancer and Nutrition (EPIC) project, which includes over 500,000 men and women aged 35 to 69 years with full dietary data and available blood samples from 10 different European countries, is a suitable framework for such studies. However, average intake of soy (and soy products) in Western populations is low, therefore variations in concentrations may be too small to detect meaningful differences between cases and controls. Lignans are more widespread in foods habitually consumed by Western populations and their intake is generally higher, therefore they may prove to be more important in cancer prevention when Western populations are concerned. As number of stored blood samples is limited, it is important to first study the variation in plasma levels of these phytoestrogens throughout Europe and only then consider further nested case-control studies. We propose to study plasma concentrations of the well-studied isoflavones genistein, daidzein, glycetein and equol and the lignans enterolactone and enterodiol in a sub-sample of EPIC participants, with emphasis on differences of gender, geographical and habitual diet, in order to determine the variation in exposure. The proposed study is cross-sectional. Study subjects will consist of around 1,600 randomly selected EPIC participants from 17 different geographical European regions. Demographic and detailed dietary data (which could be further used in future studies), as well as blood samples, will be available for each participant. Plasma levels of phytoestrogens will be determined for each participant by the Gas- and Liquid-chromatography Mass-Spectrometry (GC-MS, LC-MS) methods, in the MRC Dunn Human Nutrition Unit lab in Cambridge, the UK. We will describe the plasma means and standard deviations for each phytoestrogen, and study the influences of age, sex, region, habitual diet and possibly other factors on plasma levels of these phytoestrogens. This pilot study will determine whether the variation of phytoestrogen concentrations in the European EPIC population is sufficient to justify further large-scale prospective nested case-control studies.